This invention relates to pneumatic tire and wheel rim assemblies, and more particularly to pneumatic tire and wheel rim assemblies which are capable of continued operation even after accidental deflation of the tire or of reducing the deleterious effects of such deflation.
If an ordinary tire is deflated and continued operation is attempted, the interior surfaces of the flattened tire will rub against one another and generate a great amount of heat which leads to rapid destruction of the tire. Tire engineers have long known that this destruction can be prevented or at least postponed significantly if, for example, a lubricant is present within the so-called "inflation cavity" of the tire and rim assembly (the space bounded by the tire and the rim). The lubricant reduces the amount of friction between the interior surfaces of the tire. A great number of effective lubricants are known to those skilled in the art, including water, oils, alcohols, and silicones.
Also, material desired to be placed within the inflation cavity may include a puncture sealant composition, and it may also include chemicals which, when mixed together, generate a gas to at least partially reinflate the tire. Such puncture sealant compositions and chemicals which react to produce gas when mixed are well known to those skilled in the art.
The particular composition and/or chemicals to be placed within the inflation cavity of the tire and rim assembly is a matter of choice, dependent upon the desired properties and mode of action of such materials or combinations thereof. The term "material" will be used in this disclosure as a generic term embracing all composition and chemicals or combinations of same which may be desirably placed into the inflation cavity of a tire for release upon deflation of the tire.
Although the material can be simply placed within the inflation cavity of the tire and rim assembly when the tire is mounted to the rim, such placement is subject to several disadvantages. First, more volatile components of the material may permeate and diffuse out through the walls of the tire. Second, while the assembly is standing still, the material may settle to one or more spots on the circumference of the tire. The concentrated masses of the material at such spots would throw the entire assembly out of balance. Finally, materials intended to react in a desired fashion only upon deflation could, of course, react prematurely and undesirably if simply placed into the inflation cavity.
To overcome these disadvantages, it has been proposed to enclose material(s) in dispensing means mounted to the tire and rim assembly. The dispensing means enclose material(s) during normal operation of the tire but release same into the inflation cavity upon operation of the assembly with the tire in a deflated condition. If, for example, chemicals which react together are used, each of the components of the mixture may be contained in a separate dispensing means so that the components are mixed together when all of them are discharged into the inflation cavity upon deflation of the tire. While the use of such dispensing means provides an effective solution to the aforesaid problems, it creates a new problem: where to place the dispensing means so that they do not interfere with mounting of the tire on the rim.
This problem can best be understood in light of some description of the ordinary wheel rim and tire and the procedure used for mounting the tire on the rim. The ordinary passenger car wheel rim is a so-called "drop-center" rim. It includes a pair of radially extensive flanges at its axial extremities, a pair of axially extensive bead seats which are generally cylindrical and which are located between the aforesaid flanges, and a drop center portion located between the bead seats. The drop center is so called because it defines a "drop" or radially inwardly extending well between the bead seats. The conventional tire which is mounted on such a rim includes a pair of beads at the radially inwardmost portions of its sidewalls. These beads, which are usually reinforced with steel wire, are flexible but substantially inextensible, and have an inner diameter equal to the diameter of the bead seats. Since the diameter of the beads is less than the diameter of the flanges, it is impossible to simply slide the tire onto the rim until the beads lie on the bead seats.
Instead, a so-called "buttonhooking" procedure must be used. A portion of each bead of the tire is placed into the drop-center well. Because the drop-center well extends radially inwardly, the portions of the beads lying therein are close to the center of the wheel rim. Therefore, the opposite portions of the beads extend beyond the flanges, and can be pried over one flange.
This "buttonhooking" procedure is the most common procedure for mounting passenger car and light truck tires. Every service station attendant is familiar with this procedure and automobile manufacturers have expended substantial sums in developing automated equipment for performing it. Therefore, any change in the wheel rim assembly which would require a substantial change in tire mounting procedure would be highly undesirable.
If the drop-center well were completely occupied and filled by the material dispensing means, the beads of the tire could not be inserted into the well and the buttonhooking procedure would be impossible. The prior art has attempted to solve this problem in various ways, none of which have been truly satisfactory. U.S. Pat. No. 3,930,526 teaches the mounting of a plurality of dispensing means in the well of a drop-center rim over a small (90 degrees or less) sector of the circumference of the rim. While this structure allows the entry of the beads into the well at a point opposite from the sector where the dispensing means are mounted, it is inherently unbalanced. The entire mass of the dispensing means and the material contained therein in concentrated over one sector of the tire. To counteract this imbalance, the aforesaid patent teaches the use of an external balancing weight to be mounted opposite from the dispensing means. However, if the weight is chosen so that it exactly counterbalances the mass of the dispensing means and the material contained therein during normal operation of the tire (before release of the material from the dispensing means), the weight will inevitably be heavier than the dispensing means alone. Thus a substantial imabalance would be created when materials is released from the dispensing means into the inflation cavity and distributed throughout the tire during operation after deflation of the tire.
U.S. Pat. No. 3,942,753 teaches the use of a single dispensing means which is placed into the well and which extends around the entire circumference of the rim. So that the well can accommodate the beads of the tire during mounting, the well must be of sufficient width or axial extent to accommodate the dispensing means and the beads of the tire at the same time. Therefore the well must have a greater axial extent than would be necessary if the dispensing means were not present therein. The well will extend closer to the bead seats than would otherwise be necessary, and this, in turn, will increase the chances of the tire becoming separated from the rim during operation after deflation.